The present invention relates to snorkels, used for snorkeling and free diving, in general, and to snorkels having an inhalation tube and an exhalation tube in particular.
The snorkel as an aid to swimming and diving has been known from ancient times. Archimedes mentions an instrument for respiration which he compared to the trunk of an elephant. It appears that the Chinese used snorkels with curved tubes around 340 A.D. Leonardo da Vinci in his codex “Atlanticus” illustrated improved snorkel designs. The forerunners of the modern snorkel appeared among French spear fishermen around 1930.
The snorkel provides the ability to look downwardly into the water while breathing air from the surface. The snorkel also allows a swimmer to breathe without raising his head above the water surface, thereby reducing energy used by lifting the head above the water surface. The snorkel is also a considerable aid to free divers i.e. divers without a supplemental supply of air such as provided by a scuba tank. To understand the use of a snorkel it is necessary to consider respiration, the process whereby oxygen is supplied to the tissues of a person to sustain life. The amount of oxygen necessary to support a human depends on the level of physical activity, varying from about 300 ml per minute for a person at rest, to about 3,500 ml per minute for a person doing heavy labor. In order to maximize the amount of time which the breath can be held during a free dive, divers endeavor to lower the carbon dioxide level in the lungs and in the blood. High concentrations of carbon dioxide in the blood trigger the impulse to breathe. On the other hand, low concentrations of oxygen in the blood do not trigger the impulse to breathe, but can cause loss of consciousness. Therefore if a free diver extends the length of time during which he can hold his breath, by blowing off carbon dioxide, it is very important that physical activity be minimized to avoid exhausting the oxygen available to remain conscious.
When a person is at rest, and therefore using the minimal amount of oxygen, the amount of air inhaled and exhaled, i.e. the tidal volume, is only about 500 ml, although the typical total lung capacity is 46 liters. Of this tidal volume, approximately 150 ml is so-called “physiological dead space” i.e. air remaining in the nasal and bronchial passages which does not exchange oxygen with the blood. The 150 ml anatomical dead space amounts to about 30 percent of the total tidal volume. A typical snorkel adds a dead space of 100 to 200 ml, raising the total dead space to 50 to 70 percent of the at-rest tidal volume. This means the snorkeler must breathe more deeply than when at-rest, deep breathing in turn increases the aerobic activity, which produces fatigue and increases oxygen consumption. Increased oxygen consumption reduces the safe permissible dive time. What is needed is a snorkel with decreased dead space which functions well during free diving.